Cascaded h-bridge inverter and method for handling fault thereof

ABSTRACT

A cascaded H-bridge inverter and a method for handling a fault thereof are provided. An output voltage or an output power of each of N solar panels is detected by a controller. In a case that the output voltage of at least one of the N solar panels is lower than a preset voltage, or that the output power of at least one of the N solar panels is lower than a preset power, the controller controls a corresponding switching device to be switched off, and changes a set value of a voltage across a capacitor in the direct current side. Then, the controller controls a corresponding H-bridge module to perform inverting by taking the set value of the voltage across the capacitor in the direct current side as an input value, so that a total output modulation voltage of the cascaded H-bridge inverter meets a preset condition.

CROSS REFERENCE OF RELATED APPLICATION

This application claims the priority to Chinese Patent Application No. 201610264219.1, entitled “CASCADED H-BRIDGE INVERTER AND METHOD FOR HANDLING FAULT THEREOF”, filed with the Chinese State Intellectual Property Office on Apr. 22, 2016, which is incorporated by reference in its entirety herein.

TECHNICAL FIELD

The present disclosure relates to the technical field of power electronics, and in particular to a cascaded H-bridge inverter and a method for handling a fault thereof.

BACKGROUND

In recent years, the cascaded multi-level topology has been widely used by virtue of its excellent performance. Among all cascaded multi-level topologies, the cascaded H-bridge topology is favored due to its modular structure, simple layout, few components required to achieve the same number of levels and high system reliability.

A system structure of a current cascaded H-bridge inverter is as shown in FIG. 1. In a normal operation, solar modules are connected in parallel with the direct current side of the cascaded H-bridge inverter, and transfer the energy in the direct current side to a power grid via the cascaded H-bridge inverter. However, when a solar panel is seriously blocked or fails to work, a voltage across the solar panel will be significantly reduced, so that a voltage in the direct current side of the H-bridge inverter drops simultaneously, thereby affecting the normal operation of the system.

In the conventional technology, the corresponding H-bridge module is generally bypassed, and the remaining H-bridge modules are configured for grid-connected power generation. However, if the redundancy of the number of H-bridges cascaded in the overall system is insufficient, a total output modulation voltage of the cascaded H-bridge inverter will be reduced, and the system cannot operate stably, so that those intact solar panels are not be able to transfer energy to the power grid, thereby resulting in a significant loss of power generation.

SUMMARY

In view of the above, a cascaded H-bridge inverter and a method for handling a fault thereof are provided according to the present disclosure, to solve the problem of a loss of power generation caused by insufficient redundancy of the number of cascaded H-bridges.

To achieve the object, the technical solutions of the present disclosure are provided in the following.

A method for handling a fault of a cascaded H-bridge inverter is provided according to the present disclosure, which is applied to a cascaded H-bridge inverter. The cascaded H-bridge inverter is connected to N solar panels. The cascaded H-bridge inverter includes N capacitors, N H-bridge modules, N switching devices and a controller, where N is a positive integer. The method includes detecting, by the controller, an output voltage or an output power of each of the N solar panels. The method further includes determining, by the controller, whether the output voltage of at least one of the N solar panels is lower than a preset voltage, or whether the output power of at least one of the N solar panels is lower than a preset power. The method further includes controlling a corresponding one of the N switching devices to be switched off and changing a set value of a voltage across a corresponding one of the N capacitors in the direct current side by the controller in a case that the output voltage of at least one of the N solar panels is lower than the preset voltage, or that the output power of at least one of the N solar panels is lower than the preset power. The method further includes controlling, by the controller, a corresponding one of the N H-bridge modules to perform inverting by taking the set value of the voltage across the capacitor in the direct current side as an input value, so that a total output modulation voltage of the cascaded H-bridge inverter meets a preset condition.

Preferably, the process of the controlling the corresponding switching device to be switched off and changing the set value of the voltage across the corresponding capacitor in the direct current side by the controller may include controlling, by the controller, the corresponding switching device to be switched off, and controlling, by the controller, the set value of the voltage across the corresponding capacitor in the direct current side to be raised.

Preferably, after the process of the controlling, by the controller, the corresponding H-bridge module to perform inverting by taking the set value of the voltage across the capacitor in the direct current side as the input value, the method may further include determining, by the controller, whether the output voltage of at least one of the N solar panels is higher than the preset voltage, or whether the output power of at least one of the N solar panels is higher than the preset power, and controlling a corresponding one of the N H-bridge modules to perform inverting based on a Maximum Power Point Tracking (MPPT) control strategy and controlling a corresponding one of the N switching devices to be switched on by the controller in a case that the output voltage of at least one of the N solar panels is higher than the preset voltage, or that the output power of at least one of the N solar panels is higher than the preset power.

Preferably, before the process of the controlling the corresponding switching device to be switched off and changing the set value of the voltage across the corresponding capacitor in the direct current side by the controller, the method may further include determining, by the controller, whether the cascaded H-bridge inverter is normally connected to the N solar panels, controlling, by the controller, the cascaded H-bridge inverter to enter into an operating state, in a case that the cascaded H-bridge inverter is normally connected to the N solar panels, and controlling, by the controller, the N switching devices to be switched on.

A cascaded H-bridge inverter is provided according to the present disclosure. The cascaded H-bridge inverter is connected to N solar panels. The cascaded H-bridge inverter includes N capacitors, N H-bridge modules, N switching devices and a controller, where N is a positive integer. One output terminal of each of the N solar panels is connected to one input terminal of one of the N H-bridge modules via one of the N switching devices. The other output terminal of each of the N solar panels is connected to the other input terminal of one of the N H-bridge modules. Two input terminals of each of the N H-bridge modules are connected across a corresponding one of the N capacitors. Output terminals of the N H-bridge modules are connected in series. The controller is respectively connected to the N switching devices, the N capacitors and the N H-bridge modules. The controller is configured to detect an output voltage or an output power of each of the N solar panels, control a corresponding one of the N switching devices to be switched off and change a set value of a voltage across a one of the N capacitor sin the direct current side in a case that the output voltage of at least one of the N solar panels is lower than a preset voltage, or that the output power of at least one of the N solar panels is lower than a preset power. The controller is further configured to control a corresponding one of the N H-bridge modules to perform inverting by taking the set value of the voltage across the capacitor in the direct current side as an input value, so that a total output modulation voltage of the cascaded H-bridge inverter meets a preset condition.

Preferably, the controller may be configured to control the corresponding switching device to be switched off and changing the set value of the voltage across the corresponding capacitor in the direct current side by controlling the corresponding switching device to be switched off, and controlling the set value of the voltage across the corresponding capacitor in the direct current side to be raised.

Preferably, the controller may be further configured to control a corresponding one of the N H-bridge modules to perform inverting based on a maximum power point tracking (MPPT) control strategy and control a corresponding one of the N switching devices to be switched on, in a case that the output voltage of at least one of the N solar panels is higher than the preset voltage, or that the output power of at least one of the N solar panels is higher than the preset power.

Preferably, the controller may be further configured to determine whether the cascaded H-bridge inverter is normally connected to the N solar panels, control the cascaded H-bridge inverter to enter into an operating state, in a case that the cascaded H-bridge inverter is normally connected to the N solar panels, and control the N switching devices to be switched on after the cascaded H-bridge inverter enters into the operating state.

Preferably, each of the N switching devices may include a diode and a full control switch. An anode of the diode may be connected to a positive electrode of a corresponding one of the N solar panels, and a cathode of the diode may be connected to a corresponding one of the N capacitors and a corresponding one of the N H-bridge modules. Alternatively, a cathode of the diode may be connected to a negative electrode of a corresponding one of the N solar panels, and an anode of the diode may be connected to a corresponding one of the N capacitors and a corresponding one of the N H-bridge modules. The full control switch may be connected in parallel with the diode.

Preferably, the full control switch may be a relay or a semiconductor device.

Based on the method for handling a fault of a cascaded H-bridge inverter according to the present disclosure, the output voltage or the output power of each of the N solar panels is detected by the controller. In a case that the output voltage of at least one of the N solar panels is lower than the preset voltage, or that the output power of at least one of the N solar panels is lower than the preset power, the controller controls the corresponding switching device to be switched off, and changes the set value of the voltage across the corresponding capacitor in the direct current side. Then, the controller controls the corresponding H-bridge module to perform inverting by taking the set value of the voltage across the capacitor in the direct current side as the input value, so that the total output modulation voltage of the cascaded H-bridge inverter meets the preset condition, which avoids that the system cannot operate normally and stably and ensures that an intact solar panel can transfer energy to a power grid. Therefore, a significant loss of power generation is avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

To illustrate technical solutions according to embodiments of the present disclosure or in the conventional technologies more clearly, drawings to be used in the descriptions of the embodiments or the conventional technologies are described briefly hereinafter. Apparently, the drawings described hereinafter are only for some embodiments of the present disclosure, and other drawings may be obtained by those skilled in the art based on those drawings without creative efforts.

FIG. 1 is a schematic structural diagram of a conventional cascaded H-bridge inverter;

FIG. 2 is a flow chart of a method for handling a fault of a cascaded H-bridge inverter according to an embodiment of the present disclosure;

FIG. 3 is a flow chart of a method for handling a fault of a cascaded H-bridge inverter according to another embodiment of the present disclosure;

FIG. 4 is a flow chart of a method for handling a fault of a cascaded H-bridge inverter according to another embodiment of the present disclosure;

FIG. 5 is a schematic structural diagram of a cascaded H-bridge inverter according to an embodiment of the present disclosure; and

FIG. 6 is a schematic diagram of a control strategy of an H-bridge module according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Technical solutions of the embodiments of the present disclosure are illustrated clearly and completely in conjunction with drawings of the embodiments of the present disclosure. Apparently, the described embodiments are merely a few rather than all of the embodiments of the present disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of the present disclosure without creative efforts shall fall within the protection scope of the present disclosure.

A method for handling a fault of a cascaded H-bridge inverter is provided according to the present disclosure, to solve the problem of a loss of power generation caused by insufficient redundancy of the number of cascaded H-bridges in the conventional art.

Specifically, the method for handling a fault of a cascaded H-bridge inverter is applied to a cascaded H-bridge inverter. The cascaded H-bridge inverter is connected to N solar panels. The cascaded H-bridge inverter includes N capacitors, N H-bridge modules, N switching devices and a controller, where N is a positive integer. The method for handling a fault of a cascaded H-bridge inverter is as shown in FIG. 2 and includes steps S101 to S104.

In step S101, the controller detects an output voltage or an output power of each of the N solar panels.

When the cascaded H-bridge inverter is in a normal operating state, the controller controls the N H-bridge modules to perform inverting based on a maximum power point tracking (MPPT) control strategy based on the output voltage or the output power. When one of the N solar panels is seriously blocked or fails to work, the output voltage and the output power of the solar panel will be significantly reduced, so that a voltage in the direct current side of the corresponding H-bridge inverter drops simultaneously, thereby affecting the normal operation of the system.

In step S102, the controller determines whether the output voltage of at least one of the N solar panels is lower than a preset voltage, or whether the output power of at least one of the N solar panels is lower than a preset power.

In step S103, in a case that the output voltage of at least one of the N solar panels is lower than the preset voltage, or that the output power of at least one of the N solar panels is lower than the preset power, the controller controls a corresponding switching device to be switched off and changes a set value of a voltage across a corresponding capacitor in the direct current side, which equivalently bypasses the solar panel which is seriously blocked or fails to work, thus, the solar panel cannot output a voltage to the corresponding H-bridge module. In this case, the controller changes the set value of the voltage across the corresponding capacitor in the direct current side. To ensure the cascaded H-bridge inverter to operate stably, the set value of the voltage across the capacitor in the direct current side is preferably higher than the output voltage of the solar panel.

In step S104, the controller controls a corresponding H-bridge module to perform inverting by taking the set value of the voltage across the capacitor in the direct current side as an input value, so that a total output modulation voltage of the cascaded H-bridge inverter meets a preset condition.

The corresponding H-bridge module performs inverting by taking the set value of the voltage across the capacitor in the direct current side as the input value, so that it is ensured that the corresponding H-bridge module can provide a certain output voltage in a case that the solar panel is seriously blocked or fails to work, and thus that the total output modulation voltage of the cascaded H-bridge inverter meets the preset condition of grid-connected power generation of the cascaded H-bridge inverter, thereby ensuring that the cascaded H-bridge inverter operates stably.

Based on the method for handling a fault of a cascaded H-bridge inverter according to the embodiment, in a case that the output voltage of at least one of the N solar panels is lower than the preset voltage, or that the output power of at least one of the N solar panels is lower than the preset power, the controller controls the corresponding switching device to be switched off, and changes the set value of the voltage across the capacitor in the direct current side. Then, the controller controls the corresponding H-bridge module to perform inverting by taking the set value of the voltage across the capacitor in the direct current side as the input value, so that the total output modulation voltage of the cascaded H-bridge inverter meets the preset condition of grid-connected power generation of the cascaded H-bridge inverter, which avoids that the system cannot operate normally and stably and ensures that an intact solar panel can transfer energy to a power grid. Therefore, a significant loss of power generation is avoided.

Preferably, step S103 includes controlling, by the controller, the corresponding switching device to be switched off, and controlling, by the controller, the set value of the voltage across the corresponding capacitor in the direct current side to be raised.

In a case that the output voltage of at least one of the N solar panels is lower than the preset voltage, or that the output power of at least one of the N solar panels is lower than the preset power, the controller may compute the set value of the voltage across the corresponding capacitor in the direct current side, based on the total output modulation voltage needed by the cascaded H-bridge inverter to meet the preset condition. The controller controls the corresponding H-bridge module to perform inverting by taking the raised set value of the voltage across the capacitor (greater than the output voltage of the solar panel) as the input value, to make the total output modulation voltage of the cascaded H-bridge inverter meet the preset condition of grid-connected power generation of the cascaded H-bridge inverter.

Preferably, as shown in FIG. 3, after step S104, the method further includes steps S105 and S106.

In step S105, the controller determines whether the output voltage of at least one of the N solar panels is higher than the preset voltage, or whether the output power of at least one of the N solar panels is higher than the preset power.

In step S106, in a case that the output voltage of at least one of the N solar panels is higher than the preset voltage, or that the output power of at least one of the N solar panels is higher than the preset power, the controller controls a corresponding H-bridge module to perform inverting based on a maximum power point tracking (MPPT) control strategy and controls a corresponding switching device to be switched on.

To make the total output modulation voltage of the cascaded H-bridge inverter meet the preset condition, the solar panel which is seriously blocked or fails to work is equivalently bypassed, and the corresponding H-bridge module performs inverting by taking the set value of the voltage across the capacitor in the direct current side as the input value. The controller determines the detected output voltage and output power of each of the N solar panels. In a case that the output voltage of at least one of the N solar panels is higher than the preset voltage, or that the output power of at least one of the N solar panels is higher than the preset power, it indicates that the equivalently bypassed solar panel restores to the normal operating state and can provide the output voltage meeting the requirement. In this case, the controller may control the corresponding H-bridge module to restore to the normal operating state in which the H-bridge module performs inverting based on the MPPT control strategy, and the controller may control the corresponding switching device to be switched on.

Preferably, as shown in FIG. 4, before step S103, the method further includes steps S201 to S203.

In step S201, the controller determines whether the cascaded H-bridge inverter is normally connected to the N solar panels.

In step S202, in a case that the cascaded H-bridge inverter is normally connected to the N solar panels, the controller controls the cascaded H-bridge inverter to enter into an operating state.

In step S203, after the cascaded H-bridge inverter enters into the operating state, the controller controls the N switching devices to be switched on.

As shown in FIG. 4, step S203 is performed before step S101. However, FIG. 4 is merely an example, and step S203 may be performed in other order, as long as step S203 is performed before step S103, which is not specifically limited herein, all of which is within the scope of the present application.

Preferably, each of the N switching devices includes a diode and a full control switch. An anode of the diode is connected to a positive electrode of a corresponding solar panel, and a cathode of the diode is connected to a corresponding capacitor and a corresponding H-bridge module. Alternatively, the cathode of the diode is connected to a negative electrode of a corresponding solar panel, and the anode of the diode is connected to a corresponding capacitor and a corresponding H-bridge module. The full control switch is connected in parallel with the diode.

Preferably, the full control switch is a relay or a semiconductor device.

The switching device includes the diode and the full control switch. In a case that controller determines that the cascaded H-bridge inverter is normally connected to the N solar panels, the diode may play a role of anti-reverse connection.

After controlling the cascaded H-bridge inverter to enter into the operating state, the controller controls the N switching devices to be switched on, and may bypass the diode to reduce a voltage drop loss of the diode in an on-state.

In a case that the output voltage of at least one of the N solar panels is lower than the preset voltage, or that the output power of at least one of the N solar panels is lower than the preset power, the controller controls the full control switch in the corresponding switching device to be switched off, and changes the set value of the voltage across the corresponding capacitor in the direct current side, to ensure that the cascaded H-bridge inverter operates stably. Preferably, the set value of the voltage across the capacitor in the direct current side is higher than the output voltage of the solar panel. In this case, the diode is switched off in a reverse direction, so that the solar panel is equivalently bypassed.

A cascaded H-bridge inverter is further provided according to another embodiment of the present disclosure. As shown in FIG. 5, the cascaded H-bridge inverter is connected to N solar panels PV. The cascaded H-bridge inverter includes N capacitors C, N H-bridge modules 101, N switching devices 102 and a controller, where N is a positive integer. One output terminal of each of the solar panels PV is connected to one input terminal of one of the H-bridge modules 101 via one of the switching devices 102. The other output terminal of each of the solar panels PV is connected to the other input terminal of one of the H-bridge modules 101. Two input terminals of each of the H-bridge modules 101 are connected across a corresponding capacitor. Output terminals of the N H-bridge modules 101 are connected in series. The controller is respectively connected to the N switching devices 102, the N capacitors C and the N H-bridge modules 101.

As shown in FIG. 5, by way of example, the switching device 102 is connected between a positive electrode of the solar panel PV and the H-bridge module 101. Alternatively, the switching device 102 may be connected between a negative electrode of the solar panel PV and the H-bridge module 101, and in this case, an installation direction of the switching device 102 is reversed as compared with that shown in FIG. 5, both of which are within the scope of the present application, and which is not specifically limited herein.

The detailed operating principles are described below.

The controller detects an output voltage or an output power of each of the N solar panels PV. In a case that the output voltage of at least one of the N solar panels is lower than a preset voltage, or that the output power of at least one of the N solar panels is lower than a preset power, the controller controls a corresponding switching device 102 to be switched off, and changes a set value of a voltage across a corresponding capacitor in the direct current side. The controller controls a corresponding H-bridge module 101 to perform inverting by taking the set value of the voltage across the capacitor in the direct current side as an input value, so that a total output modulation voltage of the cascaded H-bridge inverter meets a preset condition of grid-connected power generation of the cascaded H-bridge inverter.

Based on the cascaded H-bridge inverter according to the embodiment, in a case that the output voltage of at least one of the N solar panels is lower than the preset voltage, or that the output power of at least one of the N solar panels is lower than the preset power, the controller controls the corresponding switching device 102 to be switched off, and changes the set value of the voltage across the corresponding capacitor in the direct current side. Then, the controller controls the corresponding H-bridge module 101 to perform inverting by taking the set value of the voltage across the capacitor in the direct current side as the input value, so that the total output modulation voltage of the cascaded H-bridge inverter meets the preset condition of grid-connected power generation of the cascaded H-bridge inverter, which avoids that the system cannot operate normally and stably and ensures that an intact solar panel can transfer energy to a power grid. Therefore, a significant loss of power generation is avoided.

Preferably, the controller is configured to control the corresponding switching device to be switched off and changing the set value of the voltage across the corresponding capacitor in the direct current side by controlling the corresponding switching device to be switched off, and controlling the set value of the voltage across the corresponding capacitor in the direct current side to be raised.

Preferably, the controller is further configured to control a corresponding H-bridge module to perform inverting based on a maximum power point tracking (MPPT) control strategy and control a corresponding switching device to be switched on, in a case that the output voltage of at least one of the solar panels is higher than the preset voltage, or that the output power of at least one of the solar panels is higher than the preset power.

The control strategy used by the N H-bridge modules 101 to perform inverting is as shown in FIG. 6. In a normal operating state, each of the N H-bridge modules 101 performs inverting by taking, as an input value Vdc, a direct current voltage Vdc1 outputted based on the MPPT control strategy based on an output voltage Vpv and an output current Ipv of the respective solar panel PV.

In a case that the output voltage of at least one of the N solar panels is lower than the preset voltage, or that the output power of at least one of the N solar panels is lower than the preset power, the corresponding H-bridge module 101 perform inverting by taking the set value of the voltage Vdc2 across the capacitor in the direct current side as the input value Vdc, so that the total output modulation voltage of the cascaded H-bridge inverter meets the preset condition.

In a case that the equivalently bypassed solar panel PV restores to the normal operating state and can provide the output voltage meeting the requirement, the controller may control the corresponding H-bridge module 101 to restore to the normal operating state in which the H-bridge module 101 performs inverting based on the MPPT control strategy, and the controller may control the corresponding switching device 102 to be switched on.

Preferably, the controller is further configured to determine whether the cascaded H-bridge inverter is normally connected to the N solar panels PV. The controller is further configured to control the cascaded H-bridge inverter to enter into an operating state in a case that the cascaded H-bridge inverter is normally connected to the N solar panels PV, and control the N switching devices 102 to be switched on after the cascaded H-bridge inverter enters into the operating state.

Preferably, as shown in FIG. 5, each of the switching devices 102 includes a diode and a full control switch. An anode of the diode is connected to a positive electrode of the corresponding solar panel, and a cathode of the diode is connected to the corresponding capacitor and the corresponding H-bridge module, as shown in FIG. 5. Alternatively, the cathode of the diode is connected to a negative electrode of the corresponding solar panel, and the anode of the diode is connected to the corresponding capacitor and the corresponding H-bridge module. The full control switch is connected in parallel with the diode.

A connection direction of the diode is an installation direction of the switching device. As shown in FIG. 5, the switching device is connected between the positive electrode of the solar panel and the H-bridge module. In a case that the switching device is connected between the negative electrode of the solar panel PV and the H-bridge module 101, the cathode of the diode is connected to the negative electrode of the corresponding solar panel, and the anode of the diode is connected to the corresponding capacitor and the corresponding H-bridge module, both of which are within the scope of the present application, with the implementation being determined according to the specific application environment.

Preferably, the full control switch is a relay or a semiconductor device.

The detailed operating principles of this embodiment are similar to the above embodiments, which are not repeated herein.

The embodiments of the present disclosure are described in a progressive manner and each embodiment places emphasis on the difference from other embodiments. Therefore, one embodiment can refer to other embodiments for the same or similar parts. Since the device according to the embodiment corresponds to the method disclosed in the embodiments, the description of the device is simple, and correlation parts can refer to the parts of the method.

According to the description of the disclosed embodiments, the present disclosure can be implemented or used by those skilled in the art. Various modifications made to these embodiments may be obvious for those skilled in the art, and a normal principle defined in the present disclosure may be implemented in other embodiments without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure is not limited to the embodiments described herein but confirms to a widest scope in accordance with principles and novel features disclosed in the present disclosure. 

1. A method for handling a fault of a cascaded H-bridge inverter, comprising: in the cascaded H-bridge inverter connected to N solar panels and comprising N capacitors, N H-bridge modules, N switching devices and a controller, with N being a positive integer, detecting, by the controller, an output voltage or an output power of each of the N solar panels; determining, by the controller, whether the output voltage of at least one of the N solar panels is lower than a preset voltage, or whether the output power of at least one of the N solar panels is lower than a preset power; controlling a corresponding one of the N switching devices to be switched off and changing a set value of a voltage across a corresponding one of the N capacitors in the direct current side by the controller, in a case that the output voltage of at least one of the N solar panels is lower than the preset voltage, or that the output power of at least one of the N solar panels is lower than the preset power; and controlling, by the controller, a corresponding one of the N H-bridge modules to perform inverting by taking the set value of the voltage across the capacitor in the direct current side as an input value, so that a total output modulation voltage of the cascaded H-bridge inverter meets a preset condition.
 2. The method according to claim 1, wherein the process of the controlling the corresponding switching device to be switched off and changing the set value of the voltage across the corresponding capacitor in the direct current side by the controller comprises: controlling, by the controller, the corresponding switching device to be switched off; and controlling, by the controller, the set value of the voltage across the corresponding capacitor in the direct current side to be raised.
 3. The method according to claim 1, wherein after the process of the controlling, by the controller, the corresponding H-bridge module to perform inverting by taking the set value of the voltage across the capacitor in the direct current side as the input value, the method further comprises: determining, by the controller, whether the output voltage of at least one of the N solar panels is higher than the preset voltage, or whether the output power of at least one of the N solar panels is higher than the preset power; and controlling a corresponding one of the N H-bridge modules to perform inverting based on a maximum power point tracking control strategy and controlling a corresponding one of the N switching devices to be switched on by the controller, in a case that the output voltage of at least one of the N solar panels is higher than the preset voltage, or that the output power of at least one of the N solar panels is higher than the preset power.
 4. The method according to claim 1, wherein before the process of the controlling the corresponding switching device to be switched off and changing the set value of the voltage across the corresponding capacitor in the direct current side by the controller, the method further comprises: determining, by the controller, whether the cascaded H-bridge inverter is normally connected to the N solar panels; controlling, by the controller, the cascaded H-bridge inverter to enter into an operating state, in a case that the cascaded H-bridge inverter is normally connected to the N solar panels; and controlling, by the controller, the N switching devices to be switched on.
 5. The method according to claim 2, wherein before the process of the controlling the corresponding switching device to be switched off and changing the set value of the voltage across the corresponding capacitor in the direct current side by the controller, the method further comprises: determining, by the controller, whether the cascaded H-bridge inverter is normally connected to the N solar panels; controlling, by the controller, the cascaded H-bridge inverter to enter into an operating state, in a case that the cascaded H-bridge inverter is normally connected to the N solar panels; and controlling, by the controller, the N switching devices to be switched on.
 6. The method according to claim 3, wherein before the process of the controlling the corresponding switching device to be switched off and changing the set value of the voltage across the corresponding capacitor in the direct current side by the controller, the method further comprises: determining, by the controller, whether the cascaded H-bridge inverter is normally connected to the N solar panels; controlling, by the controller, the cascaded H-bridge inverter to enter into an operating state, in a case that the cascaded H-bridge inverter is normally connected to the N solar panels; and controlling, by the controller, the N switching devices to be switched on.
 7. A cascaded H-bridge inverter, connected to N solar panels and comprising N capacitors, N H-bridge modules, N switching devices and a controller, with N being a positive integer, wherein one output terminal of each of the N solar panels is connected to one input terminal of one of the N H-bridge modules via one of the N switching devices; the other output terminal of each of the N solar panels is connected to the other input terminal of one of the N H-bridge modules; two input terminals of each of the N H-bridge modules are connected across a corresponding one of the N capacitors; output terminals of the N H-bridge modules are connected in series; and the controller is respectively connected to the N switching devices, the N capacitors and the N H-bridge modules, and the controller is configured to detect an output voltage or an output power of each of the N solar panels, control a corresponding one of the N switching devices to be switched off and change a set value of a voltage across a corresponding one of the N capacitors in the direct current side in a case that the output voltage of at least one of the N solar panels is lower than a preset voltage, or that the output power of at least one of the N solar panels is lower than a preset power, and control a corresponding one of the N H-bridge modules to perform inverting by taking the set value of the voltage across the capacitor in the direct current side as an input value, so that a total output modulation voltage of the cascaded H-bridge inverter meets a preset condition.
 8. The cascaded H-bridge inverter according to claim 7, wherein the controller is configured to control the corresponding switching device to be switched off and changing the set value of the voltage across the corresponding capacitor in the direct current side by controlling the corresponding switching device to be switched off; and controlling the set value of the voltage across the corresponding capacitor in the direct current side to be raised.
 9. The cascaded H-bridge inverter according to claim 7, wherein the controller is further configured to control a corresponding one of the N H-bridge modules to perform inverting based on a maximum power point tracking control strategy and control a corresponding one of the N switching devices to be switched on, in a case that the output voltage of at least one of the N solar panels is higher than the preset voltage, or that the output power of at least one of the N solar panels is higher than the preset power.
 10. The cascaded H-bridge inverter according to claim 7, wherein the controller is further configured to determine whether the cascaded H-bridge inverter is normally connected to the N solar panels, control the cascaded H-bridge inverter to enter into an operating state in a case that the cascaded H-bridge inverter is normally connected to the N solar panels, and control the N switching devices to be switched on after the cascaded H-bridge inverter enters into the operating state.
 11. The cascaded H-bridge inverter according to claim 7, wherein each of the N switching devices comprises a diode and a full control switch, an anode of the diode is connected to a positive electrode of a corresponding one of the N solar panels, and a cathode of the diode is connected to a corresponding one of the N capacitors and a corresponding one of the N H-bridge modules; or a cathode of the diode is connected to a negative electrode of a corresponding one of the N solar panels, and an anode of the diode is connected to a corresponding one of the N capacitors and a corresponding one of the N H-bridge modules; and the full control switch is connected in parallel with the diode.
 12. The cascaded H-bridge inverter according to claim 8, wherein each of the N switching devices comprises a diode and a full control switch, an anode of the diode is connected to a positive electrode of a corresponding one of the N solar panels, and a cathode of the diode is connected to a corresponding one of the N capacitors and a corresponding one of the N H-bridge modules; or a cathode of the diode is connected to a negative electrode of a corresponding one of the N solar panels, and an anode of the diode is connected to a corresponding one of the N capacitors and a corresponding one of the N H-bridge modules; and the full control switch is connected in parallel with the diode.
 13. The cascaded H-bridge inverter according to claim 9, wherein each of the N switching devices comprises a diode and a full control switch, an anode of the diode is connected to a positive electrode of a corresponding one of the N solar panels, and a cathode of the diode is connected to a corresponding one of the N capacitors and a corresponding one of the N H-bridge modules; or a cathode of the diode is connected to a negative electrode of a corresponding one of the N solar panels, and an anode of the diode is connected to a corresponding one of the N capacitors and a corresponding one of the N H-bridge modules; and the full control switch is connected in parallel with the diode.
 14. The cascaded H-bridge inverter according to claim 10, wherein each of the N switching devices comprises a diode and a full control switch, an anode of the diode is connected to a positive electrode of a corresponding one of the N solar panels, and a cathode of the diode is connected to a corresponding one of the N capacitors and a corresponding one of the N H-bridge modules; or a cathode of the diode is connected to a negative electrode of a corresponding one of the N solar panels, and an anode of the diode is connected to a corresponding one of the N capacitors and a corresponding one of the N H-bridge modules; and the full control switch is connected in parallel with the diode.
 15. The cascaded H-bridge inverter according to claim 11, wherein the full control switch is a relay or a semiconductor device.
 16. The cascaded H-bridge inverter according to claim 12, wherein the full control switch is a relay or a semiconductor device.
 17. The cascaded H-bridge inverter according to claim 13, wherein the full control switch is a relay or a semiconductor device.
 18. The cascaded H-bridge inverter according to claim 14, wherein the full control switch is a relay or a semiconductor device. 